An art teacher – posing online as a woman – coerced a student at his Westchester County high school to make pornographic videos of himself, authorities charged yesterday.

And in a strange twist, the anguished boy confided what had happened to someone he felt he could trust – the teacher.

The student, identified as a boy under 16, eventually told his parents and New Rochelle police – and that led to the arrest of Frank Bauer, 29.

Bauer, who lives in The Bronx, was held yesterday on $50,000 bail.

“This is the highest betrayal of trust,” Westchester District Attorney Jeanine Pirro told The Post.

Pirro said Bauer last year struck up a friendship over America Online with the student from Salesian HS, a Catholic school where he teaches.

Bauer claimed to be an older woman in their online chats.

When the student tried to break off their relationship, authorities said, Bauer threatened to create computer images of a boy engaged in sexual activity and distribute them on the Internet and at Salesian, claiming they were of the student.

The “woman” added that if the student wanted to avoid that, he had to make a sexually explicit video of himself and leave it at school.

After the boy complied, the “woman” demanded four more videos like the first.

The student was distressed and sought out Bauer and asked his advice, Pirro said.

Bauer agreed to intercede, and even said he sent an e-mail to the “woman.”

Finally, the boy told his parents about the “woman” and the videos.

“He was very frightened and was being extorted and yet he was brave,” Pirro said.

With the help of America Online, investigators discovered the “woman” was actually a phony identity set up by Bauer.

Investigators raided Bauer’s home at 1367 Crosby Ave., where he lives with his mother and grandmother, and seized his computer as evidence.

Neighbors, former and current students, and school officials were shocked by the arrest.

“I’ve known him since he was a baby. He’s a nice guy, very polite. It can’t be true ” said next-door neighbor Catherine Genovese.

“He made a lot of sacrifices for the school,” said Salesian senior John Clinton. “This is a shock to the whole school community.”

The school issued a statement saying it had suspended Bauer and offered “all cooperation possible” to Pirro.

Bauer faces up to 15 years in prison if convicted of two felony counts of use of a child in a sexual performance and one count of extortion.